The present invention relates to the field of heat energy exchange apparatus including thermal chambers and caloric sources thereof including refrigeration, and is more particularly directed to thermal chambers with high reliability obtained by providing flow path redundance in the thermal exchange structure and versatile control of associated flow rerouting, e.g. in the evaporator tubes and associated source interconnections of an ultra-low-temperature freezer for storing critical temperature-sensitive and/or potentially harmful substances in facilities such as biomedical laboratories where high reliability is essential.
There is an increasing demand in the field of the invention for ultra high reliability thermal apparatus, especially ultra-low-temperature freezers used for storing biomedical substances. A refrigeration failure in the commercial food field can be costly in terms of food spoilage and business disruption. However such failure could be catastrophic in the biomedical field; for example if it involved a limited supply of special vaccine, stored for emergency protection of the general public, lack of immediate repair or refrigerated transportation to another site of a cooling chamber facility pending corrective action could result in a disastrous total loss of the vaccine. Refrigeration failure involving toxic substances can cause personal damage and/or set off alarms that require immediate and total building evacuation. On-site personnel rarely have the expertise to take the corrective action, so there is a critical dependancy on prompt expert response in such failures.
The functional process of cooling in refrigeration takes place in the evaporator, which is typically implemented as tubing built into the walls of the low-temperature chamber. Refrigerant entering the evaporator in liquid state at an end of the tubing xe2x80x9cboilsxe2x80x9d or evaporates, changing state from liquid to gas, thus consuming heat energy and producing the cooling effect. The gas is drawn out from the opposite end of the tubing, recompressed and condensed back to liquid state in a continuous loop process.
In a common evaporator failure mode, experienced frequently in automotive air-conditioners, heaters and radiators, a pinhole leak in the tubing itself, or at a fitting, causes loss of refrigerant or other fluid medium and this cumulative loss soon degrades the thermal process and leads ultimately to total failure, meanwhile possibly contributing to pollution from the escaping gas: in the automotive case, environmental air pollution, and/or, as in the cooling chamber case, exposing the valuable payload of critical protected substances to possible contamination.
The term xe2x80x9cchamberxe2x80x9d in the present disclosure is intended to mean any thermal chamber, ranging from ultra-low temperature freezers to warming/heating chambers, in which typically it is desired to maintain substantially constant internal temperature, independent of ambient temperature and variations thereof, by circulation of a fluid thermal agent through a heat-exchanger, typically tubing located in or near the walls of the chamber
It has been known to seek improved reliability in a heat exchange type structure such as an evaporator by providing redundancy in the form of a secondary backup unit or element that can be substituted to operate in place of the primary unit or element.
Permanently connecting multiple runs of tubing in parallel, as practiced commonly in automobile radiators, heaters and air conditioners and the like, increases the cross-sectional area and thus reduces the probability of flow restriction, however the risk of developing leakage increases with multiplicity, reducing the overall reliability.
U.S. Pat. No. 5,440,894 to Schaeffer et al for STRATEGIC MODULAR COMMERCIAL REFRIGERATION discloses a commercial refrigeration network with a plurality of multiplexed compressors, condenser and associated high side and low side refrigerant delivery and suction conduits and including a remote cooling source.
U.S. Pat. No. 6,490,877 to Bash et al for MULTI-LOAD REFRIGERATION SYSTEM WITH MULTIPLE PARALLEL EVAPORATORS discloses the principle of independently metering the flow of refrigerant into each of a plurality of evaporators for the purpose of maintaining constant temperature despite heat load fluctuations.
U.S. Pat. No. 5,947,195 to Sasaki for MULTI-TUBE HEAT EXCHANGER AND AIR CONDITIONER HAVING THE SAME discloses a multi-tube heat exchanger including a pair of tanks and a large plurality of heat transfer tubes fluidly interconnected between the tanks for reducing the size of the heat exchanger and the associated air conditioner for vehicles, with air flow directed in either direction between a single duct and a plurality of branched ducts.
It is a primary object of the present invention to provide increased reliability in a thermal exchange structure such as a refrigeration evaporator in an ultra-low-temperature chamber of the type used for storing and preserving biomedical substances.
It is a further object to attain high reliability by providing redundancy and ease of substitution in the tubing structure of an evaporator in the event of leakage.
It is a further object to provide flexibility in deployment of redundant tubing sections in the evaporator to offer alternative configurations to satisfy differing needs and situations.
It is a further object to provide interface hardware units structured to facilitate manual and automatic redirection of refrigerant to redundant sections in the evaporator as well as capability of source-swapping, thus providing high system reliability through total redundancy that can be readily deployed by non-expert owner-operators without disruption or impairment of system operation.
The foregoing objects have been met in the invention of a thermal tubing structure that provides a thermal exchange system, such as an evaporator, with multi-tube redundancy for high reliability in a thermal chamber such as a freezer.
A cluster of parallel multiple continuous-length tubing runs, typically three tubes attached side-by-side, is formed in a manner to be built into the walls of the chamber or attached to a false plenum lining the inside walls of the chamber. The tube ends are fitted with a pair of versatile valve-manifold units, one at each end, that provide versatility for interconnecting to the associated thermal source(s) such as a compressor/condenser unit, with capability of rapid automatic rerouting to another tube in case of failure of any one of the tubes.
For ultra-low-temperature freezers such as those for storing bio-medical materials, the multi-tube evaporator of the present invention facilitates operations such as defrosting and refrigerant operations such as purging and replacing refrigerant, or flushing with a cleansing fluid without interrupting the required cooling process.
The multi-tube evaporator and valve-manifold system enhances ultimate reliability for low temperature systems entrusted with critical at-risk payloads, and enhances an inexpert owner-operators capability of keeping such systems operating within specification with a minimum of requirement for outside expert assistance, thus avoiding the costs, uncertainties and other disadvantages of reliance on outside experts.